Heat Pumps/ERVs/Pumps-all avgs?

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I am working on a Gym/Exercise facility with a pool.  My HVAC system has 20 Heat Pumps, 6 Energy Recovery Units, 4 heat exchangers, 35 pumps, a dehumidifyer, 3 expansion tanks and 3 boilers.  I called Trace help to confirm that like with a Geothermal system the heat pumps must be averaged if they are going to share the same water loop. 

Also as usual, this means I can not even remotely accurately represent the sytem that was designed as only some heat pumps have water side economizers, some fans/pumps are variable, etc.  I can't reflect 4 ERVs in one Heat Pump system.  I certainly will have difficulty representing the differing figures for the pumps, etc.  This is a Taco Load Match system with a pump per heat pump.

The suggestions from CDS help was to either average everything (this is a suck and does not reflect the system even remotely in my opinion!) or to create 20 different plants but just know that they won't share a loop.  Well that also doesn't cut it. 

Anyone have any helpful ideas?  I don't understand why HAP can accurately reflect more than one heat pump on a Loop but Trace can not.  This is not impossible and its beginning to really piss me off.  Every single model I have done has had heat pumps in it and I have never been able to reflect the time, energy and savings the engineers work hard to design.  Very frustrated today. 



calipidgious's picture
TRACE 700 User
Joined: 2011-03-17
Reputation: 0

Your comment cracked me up. "this is suck" - that basically sums it up.

Basically, you are correct in that this is suck, but there might be a way to do this. As I recall from a different complaint, TRACE only uses 1 ground loop in a file. With the new options of editing the ground loop, I suppose one could alter the ground loop to act as a regular water loop. Then, separate plants could be modeled which would really share a loop.

However, the "shared" ground loop may have been resolved when the ground components were updated. You could either do some experimental runs or call CDS to find out more information, but they probably will take a while to find out - as they will probably have to ask the programmers.

Bob's picture
Joined: 2010-06-30
Reputation: 475

You didn't mention what your ERV's are hooked up to. Are they off a Water-2-Water HP with the source side connected to your wellfield? Are you using Geothermal for Reheat after dehumidification?

There is no way to accurately model your design. That said, you will need to make some engineering judgements along the way that you can live with. My first GeoDesign in Trace700 I went with the worse EER/COP from the GSHP's. It had the benefit of building in the fluff factor into the comparison and can stand on it all day with LEED reviewers since I wasn't pulling the wool over anyones eyes. It was quicker and faster.

My next GeoDesign, I found that in the order entered (1-GSHP, 2-GSHP...n-GSHP) may not be how you'd number them in your equipment schedules, but in Trace "I think" it notes the number first (again I'm assuming), but when the simulation is running it takes the 1st entered HP criteria, then the next, and so forth....with that now think of each day in your design. Pulling days out of my back-side here but March 1st might only need 1/4 of the capacity so it will fill up the first 9HP's and not need the other 24HP's. On A day like today, the cooling system may be at it's block load total capacity for all 36HP's to be ON. ON meaning refer to your Equipment Energy Summary under cooling to see how many HP's "light-up". With that, now think of what engineering sense it would make to definitely use you Water-2-Waters first in your line-up since ventilation has precedence over secondary cooling, so put them in (if you have them in your design), then in my opinion would start with the worse HP's EER/COP, and end with the best EER/COP. Basically ignore that this GSHP goes to this Zone, and this GSHP goes to that Zone. That was dealt with in the 1st couple steps of the energy loads. We're in the plants now, so look at it from the wellfield's point of view now...I got water at a certain temp coming into my field, and my soil conditions say I can perform like ______. This is more tedius, but I think it is what you are looking for. It's the best way with Trace700 to simulate a HP-system. And it will be a pain in the...if you have boiler back-up, DHW, etc...but I think you will feel better about the results you get than averaging the capacities and efficiencies.

I hope this is understandable. If not, please ask...

Be Sustainable -- Never let today use up tomorrow!.

Bobba_Fett's picture
Joined: 2010-10-01
Reputation: 229